The nature of enzyme action / by W.M. Bayliss.

  • Bayliss, William Maddock, Sir, 1860-1924.
Date:
1919
Catalogue details

Licence: In copyright

Credit: The nature of enzyme action / by W.M. Bayliss. Source: Wellcome Collection.

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    Osmotic Pressure. According to Einstein’s theory of Brownian movement, the truth of which has recently been shown experimently by Perrin [1908-1910] in an almost complete manner, the kinetic energy of a particle is identi¬ cal with that of a molecule of the fluid in which it is suspended and therefore with that of any other molecule. As far as osmotic pressure is concerned, therefore, particles, molecules, and ions are of equivalent effect, acting in proportion to their number in unit volume. When colloids are electrolytically dissociated, as are solutions of many dye-stuffs and salts of proteins, the ions must be responsible for a large part of the very considerable osmotic pressure shown by such colloids (Roaf [1910], Bayliss [1909]). Since the organic ion arising from the electrolytic dissociation of these salts cannot, owing to its dimensions, pass through the parchment-paper membrane of the osmo¬ meter used, the inorganic ion is also constrained to remain inside, owing to electrostatic forces between the oppositely charged ions. The inorganic ion passes through the membrane as far as the electro¬ static forces permit, forming a layer on the outer side. Thus a “Helmholtz double layer” is produced. The relative part played by colloidal aggregates, molecules, and ions in the total osmotic pressure is governed by a complex equilibrium, which requires further investigation. If either ion were able to escape without the other, there would be established a difference of potential between the two sides of the membrane and the possibility of a perpetual motion. Action of Electrolytes. We have seen that an electrically charged colloid is able to throw down a colloid which has a charge of the opposite sign ; it is therefore not surprising to find that electrolytes have the same kind of effect. Arsenious sulphide, being negative, is precipitated by positive ions. Ferric hydroxide, being positive, is precipitated by negative ions. Now of course in adding an electrolyte, sodium chloride, for example, we are adding both positive and negative ions, which will have opposite effects. In point of fact, in these comparatively simple cases the ion which pre¬ cipitates is found to be prepotent. How do we know that it is the one of opposite sign ? The answer is by comparing the effects of series of salts with common kation or anion respectively. The chloride, sulphate, and phosphate of sodium are nearly equal in action on negative colloids, whereas on positive colloids the effect of the sulphate is considerably more than double that of the chloride, and that of the phosphate very much more than three times. 3